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Let 4x^(2)-4(alpha-2)x + alpha-2=0(alpha...

Let `4x^(2)-4(alpha-2)x + alpha-2=0(alpha in R)` be a quadratic equation. Find the values of `alpha` for which
One root is greater than `(1)/(2)` and other is smaller than 0

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To solve the problem, we need to analyze the quadratic equation given by: \[ 4x^2 - 4(\alpha - 2)x + (\alpha - 2) = 0 \] We want to find the values of \( \alpha \) such that one root is greater than \( \frac{1}{2} \) and the other root is smaller than \( 0 \). ### Step 1: Identify the coefficients The coefficients of the quadratic equation are: - \( a = 4 \) - \( b = -4(\alpha - 2) = -4\alpha + 8 \) - \( c = \alpha - 2 \) ### Step 2: Use the quadratic formula The roots of the quadratic equation can be found using the quadratic formula: \[ x = \frac{-b \pm \sqrt{D}}{2a} \] where \( D \) is the discriminant given by \( D = b^2 - 4ac \). ### Step 3: Calculate the discriminant We need to ensure that the discriminant \( D \) is greater than \( 0 \) for the quadratic to have real roots: \[ D = (-4\alpha + 8)^2 - 4 \cdot 4 \cdot (\alpha - 2) \] Calculating \( D \): \[ D = (16\alpha^2 - 64\alpha + 64) - 16(\alpha - 2) \] \[ D = 16\alpha^2 - 64\alpha + 64 - 16\alpha + 32 \] \[ D = 16\alpha^2 - 80\alpha + 96 \] Setting \( D > 0 \): \[ 16\alpha^2 - 80\alpha + 96 > 0 \] ### Step 4: Solve the inequality To find the roots of the quadratic equation \( 16\alpha^2 - 80\alpha + 96 = 0 \), we can use the quadratic formula: \[ \alpha = \frac{-b \pm \sqrt{D}}{2a} = \frac{80 \pm \sqrt{(-80)^2 - 4 \cdot 16 \cdot 96}}{2 \cdot 16} \] \[ = \frac{80 \pm \sqrt{6400 - 6144}}{32} \] \[ = \frac{80 \pm \sqrt{256}}{32} \] \[ = \frac{80 \pm 16}{32} \] Calculating the roots: \[ \alpha_1 = \frac{96}{32} = 3, \quad \alpha_2 = \frac{64}{32} = 2 \] ### Step 5: Determine the intervals The roots divide the number line into intervals. We need to test the intervals \( (-\infty, 2) \), \( (2, 3) \), and \( (3, \infty) \) to see where \( 16\alpha^2 - 80\alpha + 96 > 0 \). 1. For \( \alpha < 2 \): Choose \( \alpha = 0 \) \[ 16(0)^2 - 80(0) + 96 = 96 > 0 \] 2. For \( 2 < \alpha < 3 \): Choose \( \alpha = 2.5 \) \[ 16(2.5)^2 - 80(2.5) + 96 = 16(6.25) - 200 + 96 = 100 - 200 + 96 = -4 < 0 \] 3. For \( \alpha > 3 \): Choose \( \alpha = 4 \) \[ 16(4)^2 - 80(4) + 96 = 256 - 320 + 96 = 32 > 0 \] Thus, the intervals where \( D > 0 \) are \( (-\infty, 2) \) and \( (3, \infty) \). ### Step 6: Check conditions for roots Next, we need to check the conditions for the roots: 1. **Condition 1**: One root must be greater than \( \frac{1}{2} \). 2. **Condition 2**: The other root must be less than \( 0 \). Using Vieta's formulas, the sum of the roots \( r_1 + r_2 = -\frac{b}{a} = \frac{4\alpha - 8}{4} = \alpha - 2 \) and the product of the roots \( r_1 r_2 = \frac{c}{a} = \frac{\alpha - 2}{4} \). ### Step 7: Analyze the roots To satisfy the conditions: - \( r_1 > \frac{1}{2} \) and \( r_2 < 0 \) implies \( r_1 + r_2 < \frac{1}{2} \) (since one root is positive and the other is negative). Thus, we need: \[ \alpha - 2 < \frac{1}{2} \implies \alpha < \frac{5}{2} \] ### Step 8: Combine conditions Now we combine the conditions: - From the discriminant: \( \alpha < 2 \) or \( \alpha > 3 \) - From the roots condition: \( \alpha < \frac{5}{2} \) The only feasible solution is: \[ \alpha < 2 \] ### Conclusion The values of \( \alpha \) for which one root is greater than \( \frac{1}{2} \) and the other is smaller than \( 0 \) are: \[ \alpha \in (-\infty, 2) \]
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FIITJEE-QUADRATIC EQUATION & EXPRESSION -ASSIGNMENT PROBLEMS (SUBJECTIVE) Level - II
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